Pressure limiting devices for hydraulic brakes



Dec. 26, 1967 i M. GUETTIER PRESSURE LIMITING DEVICES FOR HYDRAULIC BRAKES Fi-led Jan; 23,

mm/ 1 m |/ni\ 2 I 7. 2 2 w? W w M 2 1 :5 E 1 .m R 4 m i m United States Patent 3,359,729 PRESSURE LIMITING DEVICES FOR HYDRAULIC BRAKES Michel Guettier, Billancourt, France, assignor to Regie Nationale des Usines Renault, Billancourt, Hauts-de- Seine, France Filed Jan. 23, 1967, Ser. No. 611,123 Claims priority, application France, Jan. 31, 1966, 47,785, Patent 89,552 2 Claims. (Cl. 6054.5)

ABSTRACT OF THE DISCLOSURE A pressure limiting device for hydraulic brakes wherein the rear wheel brake circuit is closed by a valve member when a preselected critical pressure is surpassed. The device includes an elastically deformable member, such as a piston, movable against the resistance of a spring mounted in the pressure limiting device and responsive to feed pressure. The device is characterized in that the piston is a plunger piston with a spring having a diameter greater than that of the plunger piston.

This invention relates to a modified form of embodiment of the pressure limiting device for hydraulic brakes which constitutes the subject-matter of the Patent No. 3,251,186 of May 17, 1966 and assigned to the common assignee.

The pressure limiting device disclosed in this prior patent comprises as a rule a valve member inserted according to a known disposal between the feed member and the rear-wheel brake circuit, this valve member being closed when a pre-selected critical pressure is overstepped; this invention contemplates more particularly the arrangement of a resiliently deformable member between the feed inlet and the liquid mass isolated by the closing of said valve member. The feed pressure is then transmitted only partially to the rear-wheel brake circuit and according to a law governed by the inherent characteristic of said resiliently deformable member.

In the form of embodiment illustrated in FIGURE 3 of the aforesaid patent the resiliently deformable member consists of a piston movable against the elastic resistance of a spring. When the feed pressure has attained a preselected value the valve is closed and thereafter any increment in the feed pressure is attended by a movement of said piston against the resistance of said spring. As a result, the pressure increase in the rear-wheel brake circuit is reduced with respect to the increase in the feed pressure. This invention is concerned more particularly with a modified form of embodiment of this arrangement, wherein a plunger-type piston is substituted for the ordinary piston, whereby an antagonistic spring of considerably greater diameter can be used while aifording the requisite flexibility characteristics under far better fatigue conditions for this spring.

This invention is also concerned with other improvements in connection with various details which will be set forth hereinafter as the following description proceeds with reference to the accompanying drawings in which:

FIGURE 1 reproduces FIGURE 3 of the aforesaid prior patent;

FIGURE 2 illustrates in section a modified form of embodiment of the arrangement of FIGURE 3 of the prior patent wherein a reduced pressure is transmitted to the rear brakes with the assistance of a piston movable against the resilient resistance of a spring housed in the valve member or body, and

FIGURE 3 illustrates diagrammatically a device of the type shown in FIGURE 1, wherein the valve portion is separated from the piston-containing portion.

Referring to FIGURE 1 it will be seen that in this figure the movable valve member205 guided in a cylindrical bore 206 is urged to its open position by a coil compression spring 207 as long as the feed pressure remains below a predetermined value.

At its end opposite to the guided end portion the valve member 205 has a cylindrical hollow extension 215 slidably engaged by a piston 216 normally urged away from the valve member 205 by another coil compression spring 217.

The inner cavity of said cylindrical extension 215 communicates through ducts 218 and 219 with an annular chamber 220 formed in the body 201 of the device, radial ducts 210 opening into this chamber 220 and connecting same to outlets 211 leading to pipe lines for supplying brake fluid to the rear-wheel brake circuit.

When the feed pressure has attained a preselected value depending on the force of spring 207, the valve member 205 cuts off the communication between the inlet port 204 and outlet ports 211, that is, between the feed line and the rear-wheel brake circuit.

Under these conditions, any increment in the feed pressure is attended by a displacement of piston 216 against its antagonistic spring 217. The effort resulting from the infeed pressure increment is thus partially absorbed by the action of compression spring 217, whereby the increase in the fluid pressure obtained in the rearwheel brake circuit is reduced with respect to the feed pressure increment.

Of course, the spring 217 may be so dimensioned, shaped and calculated that the ratio of the fluid pressure in the rear-wheel brake circuit to the feed pressure increment is not linear.

In the construction constituting the subject-matter of this invention and as shown more particularly in FIG- URE 2, the valve member 205 guided in the cylindrical bore 206 is urged to its open position by the coil compression spring 207 as long as the feed pressure remains below a predetermined value. At its end opposite to its guided end the valve member 205 comprises a hollow cylindrical extension 215 in which a plunger-type piston 116 is slidably mounted against the action of a coil compression spring 217. The inner space of cylinder 215 is connected through ducts 218 and 219 to the annular chamber 220 of the body 201 of the pressure limiting device, radial ducts 210 opening into this chamber and leading externally to ports 211 adapted to be connected to the pipe lines leading to the rear-wheel brakes. Hydraulic fluid is directed through the inlet port 204 is connected to the outlet ports 210 through the annular space formed between the bore of body 213 and the outer wall of extension 215, chamber 220 and radial ducts 210.

Under these conditions, it will be seen that when the feed pressure has attained a predetermined value depending on the force of spring 207, the valve member 205 is closed and cuts off the communication between the inlet 204 and outlets 211.

Any pressure increment taking place subsequently produces a displacement of the plunger piston against the elastic resistance of spring 217. The effort resulting from this pressure increment is thus partially absorbed by the distorsion of spring 217. As a result, the pressure i11- crement in the rear-wheel brake circuit is reduced with respect to the pressure increment in the supply pressure.

In this arrangement, the substitution of a plunger piston for the conventional piston of the aforesaid prior patent is advantageous in that it permits the use of an antagonistic spring 217 of greater diameter than that of piston 116, thus facilitating the manufacture of this spring and permitting obtaining the necessary flexibility characteristics under better fatigue conditions for the spring metal.

FIGURE 3 illustrates diagrammatically a modified form of embodiment of the mounting of the preceding apparatus, wherein the valve-forming portion is separated from the portion containing the plunger piston; in this case, the two portions are mounted in parallel between the supply fluid inlet and the outlet leading to the rear-wheel brake circuit.

The valve-forming portion comprises the valve member 205 allowing the supply fluid fed through the inlet 221 to flow through the duct 223 and cavity 205 (in the open valve position) to outlet 222 leading to the rear-wheel brake circuit.

Regarding the portion containing the plunger piston 116, the latter is movable in an intermediate partition of body 203, the coil compression spring 217 being housed in the cavity of said body 203 which has an outlet 224.

The supply fluid, when the valve member is open, flows along the path ABBC-CD, penetrates into the pressure limiting device at 221 and emerges therefrom at 222, then follows the path EFFGGH leading to the rear-wheel brake circuit. When the valve member 205 is closed, one fraction of the fluid flows into the body 203 at 225, drives the plunger piston 216 and the latter compresses the spring 217 t The conditions of operation are the same as in the case illustrated in FIGURE 1, but as the device is divided into two sections it is easier to house it in the space provided therefor. This arrangement also permits giving to the valve-forming member a shape which may differ, if desired, from that illustrated in FIGURE 1 and repeated in FIGURE 2.

I claim:

1. A pressure limiter for hydraulic brakes comprising a valve mechanism inserted between a master cylinder and rear wheel brake cylinders, said valve mechanism comprising a cylindrical casing having an inlet and an outlet, a cylindrical valve member and valve seat within said cylinder defining a first chamber between said valve and said inlet and a second chamber between said valve and said outlet, said valve in its open position allowing communication between said chambers, means biasing said valve open, said valve being closed by fluid pressures from the master cylinder exceeding a predetermined pressure which may be variable in the function of the load on the rear axle, an elastically deformable pressure responsive element of nonlinear characteristics connected between said input and the body of fluid which is isolated in said second chamber and said rear wheel brake cylinders by the closure of said valve, said element comprising a piston mounted in said valve member and subject to the feed pressure, spring biasing means having a diameter greater than said piston and biasing said piston against said feed pressure, whereby fluid pressures exceeding that required to close said valve are transmitted to the rear brake cylinders partly only in response to the deflection characteristics of said pressure responsive element.

2. A pressure limiting device according to claim 1 wherein said valve member is separately mounted from said pressure responsive piston, said member and said piston being mounted in parallel between a fluid inlet and outlet.

References Cited UNITED STATES PATENTS 3,251,186 5/1966 De Coye De Carstelet.

MARTIN P. SCHWADRON, Primaly Examiner.

ROBERT R. BUNEVICH, Examiner. 

1. A PRESSURE LIMITER FOR HYDRAULIC BRAKES COMPRISING A VALVE MECHANISM INSERTED BETWEEN A MASTER CYLINDER AND REAR WHEEL BRAKE CYLINDERS, SAID VALVE MECHANISM COMPRISING A CYLINDRICAL CASING HAVING AN INLET AND AN OUTLET A CYLINDRICAL VALVE MEMBER AND VALVE SEAT WITHIN SAID CYLINDER DEFINING A FIRST CHAMBER BETWEEN SAID VALVE AND SAID INLET AND A SECOND CHAMBER BETWEEN SAID VALVE AND SAID OUTLET, SAID VALVE IN ITS OPEN POSITION ALLOWING COMMUNICAION BETWEEN SAID CHAMBERS, MEANS BIASING SAID VALVE OPEN, SAID VALVE BEING CLOSED BY FLUID PRESSURES FROM THE MASTER CYLINDER EXCEEDING A PREDETERMINED PRESSURE WHICH MAY BE VARIABLE IN THE FUNCTION OF THE LOAD ON THE REAR AXLE, AN ELASTICALLY DEFORMABLE PRESSURE RESPONSIVE ELEMENT OF NONLINEAR CHARACTERISTICS CONNECTED BETWEEN SAID INPUT AND THE BODY OF FLUID WHICH IS ISOLATED IN SAID SECOND CHAMBER AND SAID REAR WHEEL BRAKE CYLINDERS BY THE CLOSURE OF SAID VALVE, SAID ELEMENT COMPRISING A PISTON MOUNTED IN SAID VALVE MEMBER AND SUBJECT TO THE FEED PRESSURE, SPRING BIASING MEANS HAVING A DIAMETER GREATER THAN SAID PISTON AND BIASING SAID PISTON AGAINST SAID FEED PRESSURE, WHEREBY FLUID PRESSURES EXCEEDING THAT REQUIRED TO CLOSE SAID VALVE ARE TRANSMITTED TO THE REAR BRAKE CYLINDERS PARTLY ONLY IN RESPONSE TO THE DEFLECTION CHARACTERISTICS OF SAID PRESSURE RESPONSIVE ELEMENT. 